begin cleanup on gps code

src/PeriodicTask.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include <Arduino.h>
+#include "configuration.h"
+
+class PeriodicTask
+{
+    /// we use prevMsec rather than nextMsec because it is easier to handle the uint32 rollover in that case, also changes in periodMsec take effect immediately
+    uint32_t prevMsec;
+
+public:
+    uint32_t periodMsec;
+
+    virtual ~PeriodicTask() {}
+
+    PeriodicTask(uint32_t period) : periodMsec(period)
+    {
+        prevMsec = millis();
+    }
+
+    /// call this from loop
+    virtual void loop()
+    {
+        uint32_t now = millis();
+        if (now > (prevMsec + periodMsec))
+        {
+            // FIXME, this lets period slightly drift based on scheduling - not sure if that is always good
+            prevMsec = now;
+
+            DEBUG_MSG("Calling periodic task\n");
+            doTask();
+        }
+    }
+
+    virtual void doTask() = 0;
+};